Thiol-terminated sulfur-containing polymers are known to be well-suited for use in various applications such as aerospace sealant compositions, due, in large part, to their fuel-resistance. Other desirable properties for aerospace sealant compositions include low temperature flexibility, short curing time (the time required to reach a predetermined strength), and elevated-temperature resistance, among others. Sealant compositions exhibiting at least some of these characteristics and containing thiol-terminated sulfur-containing polymers are described, for example, in U.S. Pat. Nos. 2,466,963, 4,366,307, 4,609,762, 5,225,472, 5,912,319, 5,959,071, 6,172,179, 6,232,401, 6,372,849, and 6,509,418. Polysulfides are also used in aerospace sealant applications where they provide high tensile strength, high shear strength, high-temperature thermal resistance, and fuel resistance, as disclosed, for example in U.S. Pat. No. 7,638,162 and U.S. Publication No. 2005/0245695.
Polythioethers that are liquid at room temperature and pressure and that have excellent low temperature flexibility and fuel resistance, such as those disclosed in U.S. Pat. No. 6,172,179, are also useful in aerospace sealant applications. For example, difunctional polythioethers having terminal hydroxyl groups prepared by reacting a hydroxyl compound with an aldehyde are described, in GB 850,178, U.S. Pat. Nos. 3,290,382, 3,959,227, and 3,997,614. Difunctional polythioethers terminated or capped with isocyanates are also known as disclosed, for example, in GB 850,178, and in U.S. Pat. Nos. 3,290,382, 3,959,227, and 3,997,614. Difunctional, i.e., linear, polythioethers, however, often swell upon prolonged exposure to hydrocarbon fuel and other lubricants. On the other hand, sealants made using polyfunctional polythioethers, can exhibit good fuel resistance, hardness and flexibility, but often with compromised adhesion and elongation.
It is desirable to provide polyfunctional polythioethers that are useful as fuel resistant and water resistant sealants with improved tensile strength and elongation, and without compromising adhesion.